In extracting hydrocarbons from the earth, it is common to drill a borehole into the earth formation containing the hydrocarbons. A drill bit is attached to a drill string, and during drilling operations, drilling fluid, or “mud” as it is also known, is pumped down through the drill string and into the hole through the drill bit. Drilling fluids are used to lubricate the drill bit and keep it cool. The drilling mud also cleans the bit, balances pressure by providing weight downhole, and brings sludge and cuttings created during the drilling process up to the surface.
Slush or mud pumps are commonly used for pumping the drilling mud. The pumps used in these applications are reciprocating pumps typically of the duplex or triplex type. A duplex pump has two reciprocating pistons that each force drilling mud into a discharge line, while a triplex reciprocating pump has three pistons that force drilling mud into a discharge line. These reciprocating mud pumps can be single acting, in which drilling mud is discharged on alternate strokes, or double acting, in which each stroke discharges drilling mud.
The pistons and cylinders used for such mud pumps are susceptible to a high degree of wear during use because the drilling mud is relatively dense and has a high proportion of suspended abrasive solids. As the cylinder in which the piston reciprocates becomes worn, the small annular space between the piston head and the cylinder wall increases substantially and sometimes irregularly. This decreases the efficiency of the pump. To reduce the effect of this wear, the cylinder typically is provided with an expendable cylinder liner.
The abrasive nature of the drilling mud translates into a relatively short lifetime of the cylinder liner and necessitates frequent replacement, placing liner manufacturing costs and efficiency in the replacement process as a primary concern. Changing a cylinder liner in a mud pump is typically a difficult, dirty, and heavy job. Further, because drilling rig time is very expensive, frequent replacement of cylinder liners causes considerable inconvenience and can be quite costly if the system and apparatus for releasing the old cylinder liners and fitting the replacement cylinder liners are slow or difficult to operate. Thus, it is important to implement the system and method for removing and replacing the cylinder liners without undue effort and downtime.
The motion of the reciprocating pump piston subjects the cylinder liner to alternating axial forces and internal pressures. The alternating internal pressures translate to alternating radial stresses in the cylinder liners that can lead to metal fatigue from the cyclic loading and sudden changes in direction of the piston motion. To counteract the effects of fatigue, radial compressive stress pre-loading is applied to the cylinder liner such that the alternating internal pressure creates less stress than the pre-load stress.
The general construction of a mud pump cylinder liner typically involves using three pieces of tubular material: a sleeve, a hull, and a collar. The sleeve forms the inside surface of the liner, the hull is assembled by shrink fit over the sleeve, and the collar is a flange ring that is shrink fit around the hull and normally retains the liner in the mud pump cylinder. The shrink fit between the sleeve and the hull creates a mechanical radial compressive stress on the sleeve and serves to counteract the effects of the alternating axial compressive forces and internal pressures on the cylinder liner which can lead to fatigue and failure of the liner.
Each piece necessary to mechanically pre-load the cylinder liner adds to the cost and weight of the liner assembly. Such a system for applying radial compressive stress pre-loading to a cylinder liner may be difficult to operate for a variety of reasons, including the involvement of heavy components, the handling of which may be dangerous for operators. Certain of these types of systems require considerable strength of operators, together with the use of lifting devices in confined spaces. Thus, the removal and replacement of a typical multi-piece liner assembly can be costly financially, and may, in some instances, subject operators to risk of injury.
Accordingly, there remains a need for new and improved systems and apparatus for installing and pre-loading cylinder liners that address certain of the foregoing difficulties.